1. Field of the Invention
This disclosure relates to a charge control device or a load driving device that have a constant current control function for a charge current or a driving current.
2. Description of Related Art
FIG. 6 shows a charge control device in accordance with the related art. The charge control device includes a first feedback loop to perform a constant current control on an adaptor current Iadp supplied from an adaptor, a second feedback loop to perform a constant current control on a charge current Ichg supplied to a secondary battery BAT, and a third feedback loop to perform a constant voltage control on a charge voltage Vbat supplied to a secondary battery EAT. These feedback loops are connected in parallel. Error amplifiers ERR1 to ERR3 are provided for the respective feedback loops. Each output of the error amplifiers ERR1 to ERR3 is provided to an output control circuit CTRL via a diode OR circuit.
As an example of a technique of the related is disclosed in Japanese patent publication No. 2000-299944.
Regarding the charge control device of the related art, if a system current Isys increases suddenly during charging of a secondary battery BAT, the adaptor current Iadp is restricted to a predetermined value by a constant current control of the adaptor current Iadp, which is controlled by the first feedback loop. Thus an over supply of current from the adopter (not illustrated) can be prevented.
However, in the charge control device of the related art, if a value of an adaptor current Iadp is restricted to a predetermined value by the first feedback loop, the charge current Ichg is restricted to a value smaller than a value set by the second feedback loop. As a result, an output of the second error amplifier ERR2 becomes an over range state to drive larger charge current Ichg in the second feedback loop.
In such a condition, if the system current Isys decreases suddenly and the constant current control on the adaptor current Iadp by the first feedback loop is finished, to increase the charge current Ichg, the constant current control on the charge current Ichg by the second loop is restarted from an over range state of the second error amplifier ERR2. Thus, there is a risk of a current larger than a predetermined value flowing through the secondary battery BAT. Therefore, a circuit to resolve the problem (e.g., a soft start circuit) is being required.
FIG. 7 shows an operation of an adaptor current Iadp, a charge current Ichg, and a system current Isys in accordance with the related art. In FIG. 7, at time t3, a constant current control of the adapter current Iadp of the first feedback loop is unlocked (not locked). Then, right after constant current control of the charge current Ichg of the second feedback loop is restarted, an overshoot of the charge current Ichg occurs.
In the foregoing description, although a charge control device is illustrated, the same problem can occur in a load driving device that has a constant current control function for driving current (e.g., LED driving device or motor driving device).